At a cold-start event, vehicles may be in open-loop fuel control until a heated exhaust gas oxygen sensor (HEGO) or sensors warm up in order to indicate a status of air-fuel ratio. During such open-loop control, tailpipe emissions may be higher than desired, as the air-fuel ratio may not be at the optimal stoichiometric air-fuel ratio (e.g. 14.7:1). Once the HEGO sensor(s) heat up to operating temperature, then open-loop control may be terminated, and closed-loop control may become active, where HEGO sensor(s) are used to adjust fueling so as to attain/maintain the optimal air-fuel ratio. Furthermore, catalytic converters on many current non-hybrid vehicles are lit off by engine combustion heat, which may take a few seconds before combustion byproduct gases may be oxidized via the catalyst.
Such issues may be exacerbated in hybrid electric vehicles (HEVs) and/or vehicles equipped with Start/Stop (S/S) capabilities, where the engine may pull down (e.g. be deactivated to stop combusting air and fuel) when vehicle speed decreases to below a threshold speed. More specifically, for HEVs and/or S/S vehicles, there may be portions of particular drive cycles where the engine may be off (e.g. not combusting air and fuel), and during such modes (e.g. electrical operation or idle stops), catalyst and/or HEGO temperature may cool to below the desired operating temperatures. Thus, in such examples, on an ensuing engine start event, there may be increased levels of emissions until the catalyst and/or HEGO sensor(s) warm up to their desired operating temperatures.
Thus, due to such issues, recent advancements to powertrains for HEVs and S/S vehicles have focused on electrically heated catalysts (EHCs) and HEGO heating elements. In other words, EHCs may include heating elements inside them in order to light off the catalyst independently of engine combustion waste heat. Similarly, HEGO heating elements may raise temperature of the HEGO sensor(s) independently of combustion waste heat.
However, HEGO heating elements, or HEGO heaters, may be prone to degradation as they are positioned in the harsh environment of the exhaust stream. When such HEGO heaters become degraded, the HEGO sensor(s) may take much longer to warm up, as the warming becomes solely reliant on engine waste heat, rather than the active heating from its own HEGO heating element. In such a case, the additional time to warm up the HEGO sensor(s) may result in increased levels of tailpipe emissions at a cold-start or under conditions where the HEGO sensor temperature has decreased to below the desired temperature at a S/S event.
The inventors herein have recognized the above-mentioned issues, and have developed systems and methods to address them. In one example, a method comprises reducing undesired emissions at a start event of an engine that propels a vehicle under conditions where a temperature of a heated exhaust gas oxygen sensor is below its desired operating temperature and where a heating element configured to heat the sensor is degraded, by providing an alternative heat source and actively routing heat from said source to the sensor to raise the temperature of the sensor to its desired operating temperature. In this way, emissions may be improved by enabling the exhaust gas oxygen sensor to reach its desired operating temperature for the start event of the engine, to enable closed-loop fuel control faster, even under conditions where the heating element configured to heat the sensor is degraded.
As one example, the start event comprises a cold-start event, and in another example, the start even comprises a start/stop event where the temperature of the sensor has decreased to below its desired operating temperature while the engine is not combusting air and fuel.
An another example, reducing undesired emissions includes reducing undesired emissions at the start event as compared to conditions where the heated exhaust gas oxygen sensor remains below its desired operating temperature for the start event.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.